The present invention relates to a reflected-light type fluorescence microscope and, more particularly, to a filter cassette used for it.
At present, reflected-light type fluorescence observation with a reflected-light type fluorescence microscope is generally popular as a means for observing the morphology of a specific substance in the cell in the field of biotechnology.
In a reflected-light type fluorescence microscope, a fluorochrome which reacts with the cells of a specimen to be observed is attached to the specimen, and excitation light having a specific wavelength corresponding to the fluorochrome is irradiated on the specimen. A specimen image formed by fluorescence generated by the excited fluorochrome is observed. In a reflected-light type fluorescence microscope, illumination light emitted from a light source along the horizontal optical axis is deflected 90xc2x0 by a dichromatic mirror, and the deflected illumination light is irradiated on the specimen. The light reflected by the specimen is transmitted through the dichromatic mirror and observed. The dichromatic mirror has a function of selectively reflecting a specific wavelength of illumination light emitted from the light source and serving as excitation light, guiding the reflected light coaxially with an observation optical axis from the rear side (image side) of an objective lens to the specimen, allowing the objective lens to form an image, and selectively transmitting a specific wavelength of fluorescence from the specimen. Therefore, the optical axis for the illumination light is shifted 90xc2x0 from the optical axis for the observation light. A dichromatic mirror inclined at 45xc2x0 with respect to the illumination optical axis and the observation optical axis is placed at the intersection of these optical axes.
Different fluorochromes are used depending on the types of cells. The wavelength of excitation light changes depending on the types of fluorochromes. Fluorescence generated by a fluorochrome has a wavelength shifted toward the longer wavelength side with respect to the excitation light. Illumination light is irradiated on a specimen through an excitation filter that transmits only light having a specific wavelength, and fluorescence light is observed through a barrier filter that transmits only the light having the specific wavelength. The excitation and barrier filters and the dichromatic mirror must be replaced depending on the types of cells to be observed.
In a conventional incident-light fluorescence microscope using a turret type filter cassette described in Japanese Utility Model Disclosure (KOKAI) No. 59-189613, Japanese Patent Publication (KOKOKU) No. 56-19605, or the like, a plurality of cubes each integrally holding and fixing a total of three optical elements, i.e., one excitation filter, one barrier filter, and one dichromatic mirror together forming a set are prepared, and these cubes are detachable from a turret. A rectangular dovetail is employed as a mechanism for attaching/detaching each cube to/from the turret because this mechanism has excellent reproducibility and facilitates attaching/detaching operation. In a prior art, a plurality (four in this case) of cubes are attached to the turret. When a fluorochrome attached to cells to be observed next is different from that attached to cells currently observed, a cube having an appropriate filter must be selected by rotating the turret, or the cubes attached to the turret must be replaced with other cubes.
As described above, the dichromatic mirror must accurately make 45xc2x0 with both the illumination optical axis and the observation optical axis; otherwise, the illumination optical axis is decentered relative to the observation optical axis to result in nonuniform illumination in the field of view. When cubes are attached to the turret or replaced, one must be careful not to disturb the above angular condition. Even if a cube attaching/detaching mechanism using a dovetail has excellent reproducibility, the absolute accuracy is determined by the machining precision of the dovetail mounting surface. To obtain a high accuracy, the dovetail must be made thick to assure rigidity. The resultant cubes become bulky, and the number of cubes that can be attached to the turret is undesirably reduced. In addition, the turret and hence the filter cassette become bulky.
Accordingly, it is an object of the present invention to provide a compact, space-saving filter cassette for a reflected-light type fluorescence microscope to which a large number of filter sets can be attached.
It is another object of the present invention to provide a filter cassette for a reflected-light type fluorescence microscope free from decentering of the illumination optical axis relative to the observation optical axis, and nonuniform illumination in the field of view.
It is still another object of the present invention to provide a compact, space-saving optical system switching mechanism having a large number of optical elements.
According to the present invention, there is provided a filter cassette detachably mounted on a fluorescent microscope, holding excitation filters, dichromatic mirrors, and barrier filters, and selecting one of the excitation filters, a corresponding one of the dichromatic mirrors, and a corresponding one of the barrier filters, the filter cassette comprising a turret having a rotation axis parallel to an optical axis for observation light, a plurality of inclined surfaces inclined at 45xc2x0 with respect to both of the rotation axis and an illumination optical axis, and through holes which extend from a top surface perpendicular to the rotation axis to the inclined surfaces and are parallel to the optical axis for the observation light, the dichromatic mirrors being mounted on the inclined surfaces, respectively, and the barrier filters being mounted on the top surfaces, respectively; and a cylindrical frame fixed around the turret to mount the excitation filters.
According to the present invention, there is provided an optical elements switching device comprising a turret having a shape obtained by cutting a sharp portion of a polyhedral pyramid having a rotation axis as a central axis along a plane perpendicular to the central axis; through holes formed to extend through a top surface of the turret and conical surfaces of the turret, a first optical path crossing the conical surfaces and a second optical path crossing the top surface; first optical elements mounted on the conical surfaces of the turret; and second optical elements mounted on the top surface. In the present specification, xe2x80x9ca top surface of the turretxe2x80x9d means a larger one of two surfaces perpendicular to the rotating axis of the turret having the above configuration.
According to the present invention, since the filters and the dichromatic mirror are directly attached to the turret, a large number of filters and dichromatic mirrors can be attached to the turret without increasing the size of the turret, thereby providing a compact, space-saving filter cassette for a reflected-light type fluorescence microscope.
According to the present invention, since the inclined surface is formed on the turret, and the dichromatic mirror is directly attached to this inclined surface, there is provided an optical elements switching device free from decentering of the illumination optical axis relative to the observation optical axis, and nonuniform illumination in the field of view.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention.
The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinbefore.